ABSTRACT
PURPOSE: Pancreatic cancer is characterized by an extremely poor prognosis due to the aggressive disease course and lack of effective therapeutic intervention. IkappaB kinase (IKK), a central kinase for nuclear factor-kappaB (NF-kappaB) activation, is often constitutively activated in pancreatic cancer cells, playing a crucial role in the malignant phenotype and resistance to anti-cancer agents. This study explored how specific inhibition of IKKbeta suppresses oncogenic proliferation of pancreatic cancer cells. EXPERIMENTAL DESIGN: We employed two different approaches, RNA interference-mediated depletion of IKKbeta (IKKbetai) and use of a novel molecularly designed IKKbeta inhibitor IMD-0354 to investigate the effects on the in vitro and in vivo growth and apoptotic response of pancreatic cancer cells. RESULTS: IKKbetai and IMD-0354 efficiently suppressed constitutive NF-kappaB activity and the growth of pancreatic cancer cells in monolayer and soft agar. IMD-0354 induced Annexin V expression, a typical apoptotic cell response. Notably, daily administration of IMD-0354 significantly suppressed tumor growth in NOD/SCID/gamma c(null) (NOG) mice without any deleterious side effect. CONCLUSIONS: These results identify IKKbeta as an attractive molecular target for pancreatic cancer therapy.
Subject(s)
Benzamides/pharmacology , Enzyme Inhibitors/pharmacology , I-kappa B Kinase/antagonists & inhibitors , NF-kappa B/antagonists & inhibitors , Pancreatic Neoplasms/enzymology , Animals , Benzamides/metabolism , Binding, Competitive , Cell Line, Tumor , Cell Proliferation/drug effects , Enzyme Activation/drug effects , Enzyme Inhibitors/metabolism , Gene Knockdown Techniques , Humans , I-kappa B Kinase/genetics , Mice , Mice, Inbred NOD , Mice, Knockout , Mice, SCID , RNA Interference , Signal Transduction , TransfectionABSTRACT
Elevated expression of c-myc has been detected in a broad range of human cancers, indicating a key role for this oncogene in tumor development. Recently, an interaction between FUSE-binding protein-interacting repressor (FIR) and TFIIH/p89/XPB helicase was found to repress c-myc transcription and might be important for suppressing tumor formation. In this study, we showed that enforced expression of FIR induced apoptosis. Deletion of the NH(2)-terminal repression domain of FIR rescued the cells from apoptosis as did coexpression of c-Myc with FIR; thus, repression of Myc mediates FIR-driven apoptosis. Surprisingly, a splicing variant of FIR unable to repress c-myc or to drive apoptosis was frequently discovered in human primary colorectal cancers but not in the adjacent normal tissues. Coexpression of this splicing variant with repressor-competent FIR, either in HeLa cells or in the colon cancer cell line SW480, not only abrogated c-Myc suppression but also inhibited apoptosis. These results strongly suggest the expression of this splicing variant promotes tumor development by disabling FIR repression and sustaining high levels of c-Myc and opposing apoptosis in colorectal cancer.
Subject(s)
Carrier Proteins/physiology , Colorectal Neoplasms/metabolism , Genes, myc/physiology , Alternative Splicing , Apoptosis/physiology , Carrier Proteins/biosynthesis , Carrier Proteins/genetics , Colorectal Neoplasms/genetics , Colorectal Neoplasms/pathology , DNA-Binding Proteins , Exons , Humans , Protein Isoforms , Protein Structure, Tertiary , Proto-Oncogene Proteins c-myc/antagonists & inhibitors , Proto-Oncogene Proteins c-myc/biosynthesis , Proto-Oncogene Proteins c-myc/genetics , RNA Splicing Factors , RNA-Binding Proteins , Repressor Proteins , Up-RegulationABSTRACT
Strong HLA-DR antigen expression on cancer cells relates to better prognosis of colorectal cancer patients, although the precise mechanism is controversial. From an immunological point of view, HLA-DR antigen, induced by interferon (IFN)-gamma, is required for tumor-associated antigen recognition by CD4(+) T cells. For instance, as reported previously, the expression of HLA-DR antigen in normal colorectal epithelium immediately adjacent to cancer coincided significantly with the existence of IFN-gamma mRNA in the tissue. From another aspect, IFN-gamma has been revealed to suppress c-myc expression in vivo through a stat1-dependent mechanism, which is important for cell growth, cell cycle and chromosome instability. In the present study, strong HLA-DR-positive expression on cancer cells was significantly related to better prognosis for colorectal cancer patients. High IFN-gamma mRNA expression in situ indicated significantly less activation of c-myc mRNA expression. Further, HLA-DR antigen expression in cancer cells, as well as Dukes stages, was an independent factor for better long-term survival by multivariate analysis. Taken together, IFN-gamma, which induces HLA-DR antigens on the cell surface, also suppresses c-myc expression in situ, and is a possible non-immunological mechanism involved in the better long-term survival of colorectal cancer patients.